Precision rectifiers generally require a common reference between the input and output of the rectifier. However, in some applications, such as precision rectifiers used in signal conditioner systems for knock sensor units associated with control circuits for internal combustion engines, the use of two different references, one for the input and one for the output, are dictated. No such device is presently available. Knock sensor units sense knocking or pre-ignition during engine operation and adjust various parameters such as timing and fuel mixture in order to minimize knocking. Knocking can be caused by a variety of factors including timing, fuel mixture, compression ratio, manifold pressure, exhaust back pressure, and fuel octane rating. Knocking is undesirable because it increases wear and decreases efficiency. A knock sensor unit uses one or more sensors to sense the vibrations caused by the knocking. The detecting of knocking is used to generate a signal which is used by the controller circuit adjust various engine parameters and reduce or eliminate the knocking. A dual reference precision rectifier would be useful in such a system and in other applications.